The invention concerns a method for regulation of the moisture profile of a paper or board web in a size press in which the paper or board web is made to run through a nip formed by the rolls in the size press, films of size being applied to the faces of the rolls in the size press by means of coating devices so that said films of size are transformed onto the paper or board web in the roll nip.
The invention also concerns a film size press, comprising a nip formed by a pair of rolls, through which nip the paper or board web is made to run and in which the rolls in the pair of rolls are provided with coating devices for spreading of size films onto the faces of said rolls, from which faces the size films are arranged to be transferred in the roll nip onto the paper or board web.
In surface sizing of paper and board, commonly a so-called short-dwell technique is used so that by means of a coating device thin size films are applied to the faces of the rolls in the size press, these size films being transferred onto the paper in the roll nip. As the members of application of the size film, as a rule, either a blade or a threaded bar or further refinements of these members are used. In blade smoothing, the thickness of the size film and, consequently, the moisture profile of the web can be regulated by altering the blade pressure. When a threaded bar is used, the thickness of the size film is regulated by varying the groove profile in the bar. In size presses, one of the most difficult problems has been the exact control of the moisture profile of the size film. By means of bar coaters, automatic regulation of the moisture profile cannot be achieved at all, because for regulation it is always necessary to replace the bar. In the blade coating technique the regulation of the moisture profile has also been very difficult, for example, because it is not always known from which side the regulation ought to be carried out.